1. Field of the Invention
This invention relates to a rotary head assembly which is adapted to displace or deflect rotary magnetic heads in directions parallel to a rotary axis to properly scan signal tracks recorded on a magnetic tape and is effectively usable for a helical scan rotary head type video tape recorder.
2. Description of the Prior Art
Recently, in order to achieve high density recording and reproduction by means of a video tape recorder using magnetic tape as a recording medium, an attempt has been made to carry out tracking control with respect to the rotary magnetic heads. In a case where the magnetic heads are displaced and driven under control of the tracking control to properly scan the recording tracks on the magnetic tape the reproduced images are free from noise bars and the like in all reproduction modes fast motion, still or slow motion reproduction mode.
Conventionally, the system of displacing the rotary magnetic heads as described above is that the magnetic heads are each mounted on a bimorph type piezoelectric element to thereby utilize the electric-to-mechanical conversion characteristic thereof to displace the magnetic heads. A bimorph type piezoelectric element has hysteresis due to the property of the material but is weak with respect to the mechanical strength. Thus, the element, when displaced in a greater amplitude, is in danger of being broken. Moreover, the characteristic changes with time. Accordingly, it is difficult to construct a deflectable rotary head assembly of adequate durability and stability. Furthermore, since this system should drive the piezoelectric element by electric signals including positional change information which are transmitted from a stationary unit to the rotary unit means of electrically conductive slip rings and brushes, there is a problem that the system becomes complicated in construction. Also, since usually a high voltage of several hundreds volts is required to displace the piezoelectric element a desired pitch, an expensive high voltage generating circuit is required.
The conventional deflectable rotary head assembly, when displaced with a large amplitude, cannot hold the magnetic heads in position perpendicular to the surface of the magnetic tape, resulting in so-called flapping. As a result, the reproduced signal levels attenuate which leads to deterioration of picture quality.
Other than the above described rotary head assembly for displacing the rotary magnetic heads, another type using electromagnetic force has been proposed. This kind of electromagnetic deflectable rotary head assembly has adequate durability and stability in operation in comparison with the assembly utilizing the electric-to-mechanical conversion characteristic of the piezoelectric element. However, the conventional electromagnetic type apparatus has not been been practical because power which is necessary to displace the magnetic heads in a required amplitude in a direction parallel to the axis of rotation becomes quite large.